Problem: If $x \otimes y = 2x-4$ and $x \triangleleft y = 2x^{2}-y^{2}$, find $(3 \otimes 1) \triangleleft -2$.
Explanation: First, find $3 \otimes 1$ $ 3 \otimes 1 = (2)(3)-4$ $ \hphantom{3 \otimes 1} = 2$ Now, find $2 \triangleleft -2$ $ 2 \triangleleft -2 = 2(2^{2})-(-2)^{2}$ $ \hphantom{2 \triangleleft -2} = 4$.